The present invention relates generally to methods and apparatus for altering material. More particularly, the present invention describes methods and apparatus for thermally altering the near surface characteristics of a material with a high energy, repetitively pulsed ion beam.
A variety of techniques have been developed for thermally altering the near surface characteristics of a material using ion beam, electron beam, x-ray and laser technologies. Unfortunately, the dramatic expectations of such technologies have largely gone unfulfilled. In particular, the use of lasers for thermally altering the near surface characteristics of materials has met with only limited commercial success. The more significant reasons for such poor reception are: 1) high cost per area treated, 2) short ( less than 50 nm) deposition depths in metals, 3) high reflectivity of metal surfaces, 4) large variations in photon absorption leading to non uniform treatment due to defects and non-uniformities in treated surfaces, and 5) low power levels require the use of small (typically xe2x89xa61 cm2) beam spots which must then be swept across a surface to treat large areas which can lead to undesirable mechanical and electrical edge effects in surfaces treated with swept beams.
The use of ion beams for thermally altering the near surface characteristics of a material, while the most promising, has been fraught with the most substantial problems. Most notable of the limitations with existing ion beam technologies have been: 1) high costs per area treated, 2) the inability to generate a large number of pulses without the costly replacement of ion beam generator components, 4) low repetition rates, 5) low average power, and 6) the inability to reliably produce a uniform ion beam of a single selectable ion species. Typical ion beam generators use dielectric surface arcing on an anode as a source of ions and thereafter magnetically or geometrically direct and focus the generated ion beam onto the material of interest. This surface arcing (also called xe2x80x9cflashoverxe2x80x9d) destroys the anode surface in  less than 100 pulses, and produces a mixed species of ions that cannot be adjusted. Other difficulties arising from flashover include: the production of large quantities of neutral gas that makes high repetition rate difficult, generated debris can contaminate surfaces being treated, and non uniformity and irreproducibility of the beam in some cases due to the localized and difficult to control nature of flashover.
Present ion beam generators are typically xe2x80x9cone shotxe2x80x9d devices, i.e. they operate at repetition rates  less than  less than 1 Hz. The principal limitations in operating existing ion beam generators at repetition rates  greater than  greater than 1 Hz are threefold. First, the inability to repetitively generate high voltage ( greater than 0.25 MeV), low impedance ( less than  less than 100 xcexa9) high average power ( greater than 109 watts), electrical pulses in the -range of 30-500 nanoseconds in duration. Second, the inability of the ion beam generator to operate repetitively for an extended number of operating cycles ( greater than  greater than 103) without replacement of major components. Third, the inability to operate with electrical efficiencies  greater than 5%. These limitations alone have made it impossible to consider industrial applications of the ion beam technology for surface treating materials.
The present apparatus for generating high energy, repetitive ion beam has over come the limitations of existing ion beam generators and provides a cost effective processing technology for thermally altering the near surface characteristics of materials.
The present invention provides a system for generating a high energy, ion beam repetitively over an extended number of operating cycles. In particular, the present invention provides an ion beam generator capable of high average power and repetitive operation over an extended operating cycle for thermally treating large surface areas of a material at low cost. The ion beam generator comprises a high energy, pulsed power system and an ion beam source both capable of high repetition rates, and both have an extended operating life. High energy, repetitively pulsed ion beams produced according to the present invention can produce surface treatments ranging from localized high temperature anneals to melting, both followed by rapid thermal quenching to ambient temperatures. In metals this can produce complex surface alloys, liquid phase mixing of layers of different materials, and/or non-equilibrium microstructures including amorphous, disordered crystalline, and nanocrystalline phases. Other applications include etching and cross-linking of polymers, surface glazing and sealing of ceramic surfaces and cost-effective dry processes for surface deburring, polishing, and cleaning without the use of solvents. The unique energy deposition in-depth characteristic of high energy, repetitively pulsed ion beams also allows this technology to be used as a new technique for bonding of films to substrates. The depth of treatment can be controllable by varying the ion energy and species as well as pulse duration or length.